Former Washington Post reporter Kovaleski has a chronic congenital musculoskeletal condition called arthrogryposis, which limits movement in his arms.

Trump has been citing a Washington Post article written by Kovaleski in 2001 to support his widely debunked claim that thousands of people in parts of New Jersey with large Arab populations celebrated the collapse of the World Trade Center towers on September 11, 2001.

Trump said: "Now the poor guy [Kovaleski] — you ought to see the guy: ‘Uhh I don’t know what I said. I don’t remember.’ He’s going, ‘I don’t remember. Maybe that’s what I said."

Kovaleski said earlier in the week that he couldn’t remember anyone ever claiming to have seen what Trump claims.

"I do not recall anyone saying there were thousands, or even hundreds, of people celebrating. That was not the case."

A spokesperson for the New York Times said it was outrageous that he would "ridicule the appearance of one of our reporters".

A petition has been set up calling on Trump to apologise. Advocacy group Ruderman Family Foundation has offered him sensitivity training to help him better understand people with disabilities

Trump has since taken to Twitter to say: "'The failing @nytimes should be focused on good reporting and the papers financial survival and not with constant hits on Donald Trump!"

Republican presidential candidate Donald Trump mocks Serge Kovaleski

While Trump's claims of thousands of people celebrating the 9/11 attacks have been debunked, witnesses did report seeing men apparently celebrating and exhibiting "puzzling behaviour".

One New Jersey resident with a view of the twin towers called the police after spotting the men who appeared to be filming the attack. The unnamed witness later recalled: "They were like happy, you know … They didn't look shocked to me.”

At the time the New York Times reported that the group of five men had set up video cameras aimed at the Twin Towers, and were seen congratulating one another afterwards.

The men were Israeli employees of a Jersey-based moving company Urban Moving Systems. The five Israeli men were later arrested and interrogated and then deported back to Israel. The boss of Urban Moving Systems Dominick Suter was also questioned by the FBI before leaving for Israel.

The men later denied they had been celebrating and told Israeli television that they were just filming in order to document the event. Channel 4 interviewed three of the men who said they were in New Jersey for a holiday.